This invention relates to a ceramic capacitor having a low power factor. More specifically, it relates to a cylindrical barium titanate capacitor having closely spaced, substantially parallel electrodes, connected in parallel, or two electrodes spiraled on its surface with a thin dielectric layer underneath each electrode.
It is known to form a capacitor by firing a barium titanate ceramic in air to mature it, thus forming an insulator or dielectric throughout its surface, and then firing in a reducing atmosphere to form a semi-conductor throughout. The electrodes are applied and fired-on; this step also produces a thin insulating or dielectric layer underneath the electrodes.
Alternatively, the ceramic may be sintered, reduced and reoxidized along the margins before the electrodes are applied. The semiconducting part of the ceramic may also be formed by suitable doping a green ceramic mix and firing in air to form both the semiconducting and dielectric zones without a reducing step. Another method involves preparing both the ceramic and the electronic mixes, assemblying, firing in air to remove organic matter, e.g. binders, and then in a reducing atmosphere with no subsequent reoxidation. In the latter case, metal electrodes melting above 1150.degree. C. are used. Commonly, these electrodes are of platinum or palladium to be able to withstand the firing temperatures and also not oxidize, although iron compositions have also been used. When the electrodes are made of gold or platinum, there is no oxidation of the ceramic material underneath; rather there is an ohmic connection.
It is also well known that electrodes of the same area have the same capacitance whether they are on the same or opposite sides of the semi-conductor. However, when the electrodes are coplanar, the resistance of the conducting path which connects two dielectric layers through the semiconductor increases because of the increased length of the path between them. Power factor is also increased with increasing path length.